1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method for forming a dual-layered metal line of molybdenum Mo/aluminum Al for an LCD device.
2. Discussion of the Related Art
In general, demand for various display devices has been steadily increasing. Accordingly, significant efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Various types of flat display devices are already currently in use.
Among the various flat display devices, the liquid crystal display (LCD) device has been most widely used due to advantageous characteristics such as thinness, light weight, and low power consumption. Accordingly, LCD devices are increasingly replacing cathode ray tubes (CRT). In addition to the mobile type LCD devices such as a display for a notebook computer, LCD devices have been developed for computer monitors, televisions receivers and information displays.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of an LCD device has been lacking in some respects as compared to other features and advantages of the LCD device. The key to developing the LCD device as a general display device in various fields lies on whether the LCD device can yield a high quality picture, such as high resolution and high luminance with a large-sized screen while still maintaining light weight, thinness, and low power consumption.
A typical LCD device includes an LCD panel for displaying a picture image, and a driving part for applying a driving signal to the LCD panel. Moreover, the LCD panel includes first and second substrates bonded to each other at a predetermined distance, and a liquid crystal layer between the first and second substrates. In this instance, the first substrate (TFT array substrate) comprises a plurality of gate lines arranged in one direction at fixed intervals, a plurality of data lines arranged at fixed intervals perpendicular to the plurality of gate lines, a plurality of pixel electrodes forming a matrix in which respective pixel regions are defined by the intersection of the plurality of gate and data lines, and a plurality of thin film transistors being switched by signals from the gate lines for transmitting signals from the data lines to the respective pixel electrodes. In addition, the second substrate (color filter array substrate) includes a black matrix layer for preventing light from reaching portions of the first substrate other than the pixel regions, and R/G/B color filter layer for displaying various colors, and a common electrode for displaying an image.
The LCD device is driven in accordance with an optical anisotropy and a polarizability of the liquid crystal. Specifically, liquid crystal molecules are aligned in accordance with directional characteristics due to the liquid crystal molecules having respectively long and thin shapes. In this respect, an electric field is applied to the liquid crystal for controlling an alignment direction of the liquid crystal molecules. Specifically, if the alignment direction of the liquid crystal molecules is controlled by the electric field, light is refracted along the alignment direction in accordance with the optical anisotropy of the liquid crystal, thereby displaying the image.
In a typical LCD device, the gate line or the data line is formed not as a single-layered structure of an aluminum Al layer, but as a dual or three-layered structure by depositing a molybdenum Mo layer or a chrome Cr layer (or molybdenum Mo) on or under the aluminum Al layer to prevent a signal delay from being generated between the lines or electrodes due to a coupling capacitance. Even though the gate or data line is formed of aluminum Al having great resistance characteristics, aluminum Al has a weak corrosion resistance to chemicals. Accordingly, when forming the gate or data line as an aluminum Al layer, it is hard to control an etch rate during an etching process. Moreover, an aluminum gate and data line may be easily oxidized, thereby causing rupture of the lines. Thus, the molybdenum Mo layer is deposited on the aluminum Al layer since molybdenum Mo has a greater corrosion resistance to chemicals, thereby preventing direct contact between the aluminum Al layer and the chemicals. If the gate or data line is formed with the dual-layer structure of the aluminum Al layer and the molybdenum Mo layer, the line is patterned using a wet-etch process. In this instance, the aluminum Al has higher etch rate than the molybdenum Mo. Accordingly, an overhang is generated in the molybdenum Mo layer on the aluminum Al layer in accordance with a Galvanic Corrosion phenomenon.
Hereinafter, a method forming a line of an LCD device in accordance with the related art will be described as follows.
FIG. 1A is a cross-sectional view illustrating a method for forming a line of an LCD device according to the related art. As shown in FIG. 1A, an aluminum Al layer 12 and a molybdenum Mo layer are sequentially deposited on a glass substrate 11. In this instance, the aluminum Al layer is formed with a thickness of 10 Angstroms to 3000 Angstroms, and the molybdenum Mo layer 13 is formed with a thickness of 10 Angstroms to 2000 Angstroms.
FIG. 1B is a cross-sectional view illustrating the method for forming a line of an LCD device according to the related art. As shown in FIG. 1B, a photoresist layer is deposited on an entire surface of the molybdenum Mo layer 13, and an exposure and developing process is performed thereon using a mask, thereby forming a photoresist pattern 14 on a predetermined portion of the molybdenum Mo layer 13.
FIG. 1C is a cross-sectional view illustrating the method for forming a line of an LCD device according to the related art. Referring to FIG. 1C, a wet-etch process of a spraying method is performed using the photoresist pattern 14 as a mask, whereby the molybdenum Mo layer 13a and the aluminum Al layer 12a are selectively removed to form a metal line pattern. In the wet-etch process, an etchant is formed of a mixed acid solution containing a ratio of 30% to 70% of phosphoric acid, 2% to 30% of nitric acid and 1% to 20% of acetic. In addition, a small amount of an additive may be added to the etchant.
Following the wet-etch process, an overhang is generated in the molybdenum Mo layer 13a in accordance with a potential difference due to a Galvanic Corrosion phenomenon between the molybdenum Mo layer 13a and the aluminum Al layer 12a. According to the Galvanic Corrosion phenomenon, if two metal layers having different electrochemical characteristics are dipped into a conductive etchant, and the two metal layers are electrically connected to each other, the lower metal layer behaves as an anode. Accordingly, the lower metal layer is first ionized. Specifically, the two metal layers have different etch rate with respect to the same etchant. Accordingly, an additional process is required to remove the overhang of the molybdenum layer 13a following the wet-etch process.
FIG. 1D is a cross-sectional view illustrating the method for forming a line of an LCD device according to the related art. As shown in FIG. 1D, an ashing process is applied to the photoresist pattern 14a to decrease the size of the photoresist pattern 14a. In addition, a dry-etch process is performed to remove the overhang of the molybdenum Mo layer 13a. The dry-etch process uses an etchant of fluorine such as SF6, thereby forming a line of the aluminum Al layer and the molybdenum Mo layer 12a and 13a having a stepwise profile. In this case, as shown in portions A of FIG. 1D, the glass substrate 11 suffers from etch damages along the circumference of the line 12a and 13a due to the etchant used in the dry-etch process.
FIG. 1E is a cross-sectional view illustrating the method for forming a line of an LCD device according to the related art. Referring to FIG. 1E, the process for forming the dual line of the aluminum Al/molybdenum Mo 12a and 13a according to the related art is completed by removing the photoresist pattern.
FIG. 2 is an SEM view illustrating a line and a substrate of an LCD device according to the related art.
The related art method for forming a line of the LCD device has the following disadvantages. As mentioned above, the dry-etch process is performed with an etchant of fluorine such as SF6 in order to remove the overhang of the molybdenum Mo layer. However, as shown in portions A of FIG. 1D, the glass substrate is etched at the portion corresponding to the circumference of the aluminum Al layer with a thickness of 660 Angstroms during the anisotropic dry-etch process. Specifically, the glass substrate is differently damaged in accordance with a size of the overhang of the molybdenum Mo layer. As the overhang of the molybdenum Mo layer increases, the glass substrate is significantly damaged. Accordingly, if the glass substrate of the LCD device having the dual-layered line structure is significantly damaged, the LCD device may eventually fail in a rework process, or the rework process may be complicated.